This invention relates to new melt-blowing processes for producing non-woven or spun-bonded mats from fiberforming thermoplastic polymers. More particularly, it relates to processes in which a thermoplastic resin is extruded in molten form through orifices of heated nozzles into a stream of hot gas to attenuate the molten resin as fibers, the fibers being collected on a receiver in the path of the fiber stream to form a non-woven or spun-bonded mat. Various melt-blowing processes have been described heretofore including those of Van A, Wente (Industrial and Engineering Chemistry, Volume 48, No. 8 (1956), Buntin et al. (U.S. Pat. No. 3,849,241), Hartmann (U.S. Pat. No. 3,379,811), and Wagner (U.S. Pat. No. 3,634,573) and others, many of which are referred to in the Buntin et al. patent.
Some of such processes, e.g. Hartmann, operate at high melt viscosities, and achieve fiber velocities of less than 100 m/second. Others, particularly Buntin et al. operate at lower melt viscosities (50 to 300 poise) and require severe polymer degradations to achieve optimum spinning conditions. It has been described that the production of high quality melt blown webs requires prior degradation of the fiber forming polymer (U.S. Pat. No. 3,849,241). At an air consumption of more than 20 lb. of air/lb. web substantially less than sonic fiber velocity is reached. It is known, however, that degraded polymer leads to poor web and fiber tensile strength, and is hence undesireable for many applications.